How does high C load affect nitrous oxide emission of subsurface wastewater infiltration system?

Subsurface wastewater infiltration systems (SWISs) have drawn much attention due to the lower operating costs, lower energy demands and absence of secondary pollutants requiring further treatment. The process of denitrification involves reduction of nitrate to nitrous oxide (N₂O) and dinitrogen gas (N₂). Though removal of nitrate is advantageous from a water quality perspective, N₂O may contribute to adverse environmental effects. This study evaluated N₂O emission at high C loading regimes. The results revealed that as the C load increased, N₂O emission increased first and then decreased, indicating that carbon source was a limiting factor for the release of N₂O from the denitrification process. Denitrification was the dominant process for the release of N₂O at any of the given C loads. When the influent carbon load was in the range of 220-460 mg/L, the contribution of denitrification to N₂O emissions came to 69.77-83.11% (feeding period) and 67.07-79.53% (rest period), respectively.